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I remain skeptical that fusion will ever be an economical or even viable source of energy. The major problems are that: 1. The Sun, by comparison, produces les

by cletus 14y ago

I remain skeptical that fusion will ever be an economical or even viable source of energy. The major problems are that: 1. The Sun, by comparison, produces less energy (per volume) than compost [1]; 2. Heavier isotopes of hydrogen, used because they provide a faster reaction, emit more neutrons, which tend to have a devastating effect on the container. Thus you have two conditions at odd: speed of the reaction vs viability of containment; 3. The Sun solves the problem of containing the reaction with gravity. Magnetism has yet to yet to be shown as viable of effective in energy terms; and 4. People focus too much on the fuel cost, which is near-zero and supply is effectively unlimited. But that's H1. Deuterium is relatively plentiful [2] but tritium is one of the most expensive substances (by mass) on Earth. Helium-3 is an alternative but is also incredibly expensive [3] such that recovering it from the Moon may actually be economically viable relative to cost (that should tell you something about how rare/expensive it is). D-D reaction research I think is currently far behind anything involving Tritium or He-3. Fuel costs aside, that's only one input into the cost equation. Even if the fuel is free the power plant will cost $X to produce, will require $Y in maintenance per year for Z years and produce W MW of power. Plug all those numbers together and that power still has cost even with "free" fuel. For automobiles at least, petrochemicals have some incredible advantages. They are relatively stable, cheap and the machinery for turning them into usable energy is cheap and mass-produced. Of course it has two major problems: 1. Emissions; and 2. It is a limited resource. I tend to think at some point in the next few centuries genetic engineering will allow us to solve (2) by sustainably "growing" more fuel with something like algae or (to borrow an idea from Anathem) "fuel trees". Of course something must be consumed to produce this energy. Battery technology will have to improve by an order of magnitude at least to be a viable alternative to fuels that are easily transported and don't require the infrastructure that charging stations otherwise would. For fixed power generation I'm really not sure what the future holds. If we're not careful we'll simply exhaust a number of readily available fuels and the population problem will "correct" (as it often does) with war. [1]: http://www.abc.net.au/science/articles/2012/04/17/3478276.htm http://www.abc.net.au/science/articles/2012/04/17/3478276.ht... [2]: http://www.ccfe.ac.uk/FAQ.aspx#Depletion http://www.ccfe.ac.uk/FAQ.aspx#Depletion [3]: http://en.wikipedia.org/wiki/Helium-3#Fusion_reactions http://en.wikipedia.org/wiki/Helium-3#Fusion_reactions

Daniel_Newby 14y ago
1. The sun is in equilibrium. Increased power would cause it to expand, and the power density is an exponential function of density. 2. You capture the neutrons with a lithium container, which produces tritium. 3. The Z-machine is an inertial confinement machine: a powerful electric arc produces a radiation pulse that compresses the fision target. 4. I suspect if you can achieve ignition with tritium, you can use the fusion flash to ignite deuterium in a two stage process.
- Daniel_Newby 14y ago
  "the fision target" I meant fusion target. Oops.
InclinedPlane 14y ago
1. The Sun uses gravitational confinement and will run for over 10 billion years, producing nearly 400 yottawatts of power all throughout that time. The relationship to the average power density of compost is utterly, utterly irrelevant. 2. Oh no, neutrons! If only we'd spent 7+ decades working with neutron reactions and their interactions with materials. It's a shame there are no functional power reactors anywhere in the world that are subjected to a high-neutron flux. 3. Magnetic confinement of fusion works just fine, we're at a point where it looks like it's simply a matter of scaling things up to get to greater than break-even energy-wise. How practical and competitive such reactors might be remains to be seen, but it's fairly unlikely that they just plain won't work. 4. The biggest advantages of fusion as an energy source are that it's safe and clean. It won't be until quite some time in the future when we have the ability to make use of something like p-B11 fusion reactions (which are far, far beyond our capability at the moment due to the much higher plasma temperatures required) when fusion will be, potentially, much cheaper and easier than competing alternatives (due to the potentially lower capital cost and conversion efficiency of an aneutronic fusion reactor which wouldn't even need a steam turbine).
- DennisP 14y ago
  Some recent modeling suggests that by using side ignition of fuel with a petawatt picosecond laser, boron fusion would only be ten times harder than D-T. By comparison, for the spherical arrangement NIF uses, boron is 100,000 times harder. Here's one paper, google brings up more: http://ocs.ciemat.es/EPS2011PAP/pdf/P5.037.pdf http://ocs.ciemat.es/EPS2011PAP/pdf/P5.037.pdf The lasers are almost good enough to try this and advancing fast. Another approach to boron ignition is focus fusion. They published a peer-reviewed paper recently showing they'd achieved the temperature required for boron fusion (they're up to 1.8 billion degrees C). They need higher density though, they're working on that and hope to get to the level they need in a year.

by cletus 14y ago

Daniel_Newby 14y ago

1. The sun is in equilibrium. Increased power would cause it to expand, and the power density is an exponential function of density. 2. You capture the neutrons with a lithium container, which produces tritium. 3. The Z-machine is an inertial confinement machine: a powerful electric arc produces a radiation pulse that compresses the fision target. 4. I suspect if you can achieve ignition with tritium, you can use the fusion flash to ignite deuterium in a two stage process.

Daniel_Newby 14y ago
"the fision target" I meant fusion target. Oops.

InclinedPlane 14y ago

1. The Sun uses gravitational confinement and will run for over 10 billion years, producing nearly 400 yottawatts of power all throughout that time. The relationship to the average power density of compost is utterly, utterly irrelevant. 2. Oh no, neutrons! If only we'd spent 7+ decades working with neutron reactions and their interactions with materials. It's a shame there are no functional power reactors anywhere in the world that are subjected to a high-neutron flux. 3. Magnetic confinement of fusion works just fine, we're at a point where it looks like it's simply a matter of scaling things up to get to greater than break-even energy-wise. How practical and competitive such reactors might be remains to be seen, but it's fairly unlikely that they just plain won't work. 4. The biggest advantages of fusion as an energy source are that it's safe and clean. It won't be until quite some time in the future when we have the ability to make use of something like p-B11 fusion reactions (which are far, far beyond our capability at the moment due to the much higher plasma temperatures required) when fusion will be, potentially, much cheaper and easier than competing alternatives (due to the potentially lower capital cost and conversion efficiency of an aneutronic fusion reactor which wouldn't even need a steam turbine).

DennisP 14y ago
Some recent modeling suggests that by using side ignition of fuel with a petawatt picosecond laser, boron fusion would only be ten times harder than D-T. By comparison, for the spherical arrangement NIF uses, boron is 100,000 times harder. Here's one paper, google brings up more: http://ocs.ciemat.es/EPS2011PAP/pdf/P5.037.pdf http://ocs.ciemat.es/EPS2011PAP/pdf/P5.037.pdf The lasers are almost good enough to try this and advancing fast. Another approach to boron ignition is focus fusion. They published a peer-reviewed paper recently showing they'd achieved the temperature required for boron fusion (they're up to 1.8 billion degrees C). They need higher density though, they're working on that and hope to get to the level they need in a year.